Of all the pipe materials currently available, steel pipes have the widest applications and uses. Steel is unique in its excellent mechanical properties and characteristics, which enable it to achieve performance levels required in even the most demanding pipeline systems for the conveyance of large volumes of water, petroleum or natural gas.

Wide Ranging Yield Strengths

Steel pipes are manufactured from a wide variety of steel to suit both internal pressure requirements and external earth and traffic loadings. The minimum yield stress of such steels varies from 207MPa to 551MPa. The design engineer thus has the choice of specifying a higher yield strength steel without increasing wall thickness and weight of the pipe to achieve the required safety factor (usually 2), or a lower one when actual internal pressure requirements and external loadings are sufficiently light, thus saving on costs.

High Carrying Capacity

Steel pipes provide exceptionally high working pressure capability.

Manufacturability

A key advantage of steel is its ability to be rolled, formed and welded, which allows it to be engineered and manufactured into pipes of various sizes, shapes and configurations.

Good Ductility/Flexibility

Steel pipes have minimum elongation values of 25% and above resulting in high ductility. This allows them to withstand stresses and strains without breaking under shock from surge, water hammer and a host of other natural and man made disturbances. This means the pipe can be cold-bent in the field or subjected to considerable overhand loads without failure.

High Modulus of Elasticity

Steel pipes have a higher modulus of elasticity (approx. 210,000 MPa) compared with other materials.

High Dimensional Tolerances

Steel pipe manufacturing has extremely tight minus thickness tolerances. For example a pipe of DN600 mm is at most 0.35mm below the nominal thickness.

No Casting Skin Effects

When assessing strength requirements, the complete wall thickness is used for steel pipes; there is no brittle surface skin, such as that resulting from casting which cannot be used for wall thickness calculations.

Good Factors of Safety

Net factors of safety of the various pipe materials have to take into account minimum elongation values, minus tolerances on thickness and the presence of a low strength casting skin. Hence the effect of tight thickness tolerance and high values of minimum elongation (25% and above) results in factors of safety ranging from 1.7 (DIN 2460) to 2.0 (AWWA C200) being specified for steel pipes.

Toughness

When steel pipes are subjected to close to or below zero operating temperatures, micro-alloying elements in steels (X52 and above) result in high values of impact strength under sub–zero conditions.

Weldability

Steel pipes can be welded easily on site resulting in a leak free joint. This is extremely useful for gas and oil lines where no leaks can be tolerated, unlike rubber compression joints.

Long Service Records

Though steel pipes were first laid as early as 1863 and the first welded steel pipe in 1887, numerous records showed that steel pipes laid more than 112 years earlier when little or no anti-corrosion coatings were available were still in service in early 1970s (Data Source: Welded Steel Pipe Manual
– American Steel Plate Fabricators Association 1970). Today with superior corrosion protection
materials available, further enhanced by a cathodic protection system, a properly maintained
steel pipeline has an indefinite life span and is inexpensive to operate.

Permanent Bottle-tight Joints

Steel pipe joints do not depend on perfect trenching grading or soil stability to maintain watertight integrity. The resilient steel pipe absorbs soil stresses without affecting joint soundness.

Economical Installation and Maintenance

Steel pipes have relatively lighter walls requiring less labour to transport and install. Longer pipe lengths also enable faster and more economical installations. Dielectric coatings and cathodic protection lead to long life spans and low maintenance as well.

Improved Lifecycle Costs

Steel is easy to transport and install because of low weight and flexibility. These characteristics reduce transportation and handling costs, and lower excavation and backfill expenses.

Stringent Testing of Pipes During Manufacturing

The manufacturing standards of steel pipes require the performance of non-destructive tests which can be applied to every pipe. All steel pipe standards specify 100% hydrostatic pressure testing to all seamless or welded pipe to as high as 90% of yield stress. Either ultrasonic flaw detection or real time X-ray of welds is also carried out. Non-destructive testing is carried out on a sampling of each batch of 50 or 100 tubes according to diameter and specifications. These tests include the chemical properties of steel, as well as the mechanical properties of the parent metal and the weld.